1. Field of the Invention
The present invention relates to a process for producing a monodisperse polymer and, more specifically, to a process for producing on an industrial scale a monodisperse polymer having a controlled molecular weight and a controlled molecular weight distribution by living anionic polymerization.
2. Description of the Related Art
It has been known for a long time that polymers having a controlled structure are obtained from conjugated dienes, vinyl aromatic compounds and (meth)acrylic acid esters by living anionic polymerization using an alkali metal or organic alkali metal.
It has also been known that an alkenylphenol polymer typically represented by p-vinylphenol is useful as a resist material, a curing agent for epoxy resins, an antioxidant and the like.
As for processes for producing alkenylphenol polymers, several processes have been proposed including: thermal radical polymerizations to give a polymer of p-vinylphenol (JP-A 53-13694, JP-A 57-44067, JP-A 57-44608, JP-A 57-44609, and JP-B 61-2683); radical polymerization of a p-vinylphenol wherein the hydroxyl group of p-vinylphenol is protected by a saturated aliphatic protecting group and a treatment with an acidic reagent follows to give a polymer of p-vinylphenol (JP-A 4-279608 and 6-298862); and an anionic polymerization of p-vinylphenol wherein the hydroxyl group of p-vinylphenol is protected by tert-butyl dimethyl silyl group and a treatment with an acidic reagent follows to give a polymer of p-vinylphenol having a sharp molecular-weight distribution [Yuki-Gosei Kagaku 44, 2, 45 (1986)]. Further, the present inventors have proposed the homopolymerization or the copolymerization of alkenylphenol wherein the hydroxyl group of alkenylphenol is protected by a saturated aliphatic protecting group and detachment of the protecting group follows to give a narrow polydispersity polymer of alkenylphenol (JP -A 3-277608 and 4-53807).
The living anionic polymerization is suitable for the synthesis of a polymer such as an oligomer having a molecular weight of several thousands and a polymer having a controlled molecular weight and a controlled molecular weight distribution can be obtained with ease by the living anionic polymerization if it is in small quantity. However, when it is adapted to the synthesis or industrial-scale production of a polymer having a molecular weight of several tens of thousand even if it is in small quantity, it is difficult to completely eliminate the effect of an active hydrogen-containing compound such as water introduced into a reaction system. Therefore, the living anionic polymerization involves the above problem to be solved for the precise control of the molecular weight of a polymer though it can control molecular weight distribution.
Recently, development of a homopolymer of a copolymer, having a phenolic hydroxyl group and a controlled structure, of alkenylphenol are desired for a resist material which achieves submicron resolution, and used for super-LSI manufacturing, as well as for a separation membrane and for a biocompatible polymeric material.
The above-mentioned polymers obtained by thermal or radical polymerization of p-vinylphenol have the following disadvantages: broad molecular weight distributions, uncontrolled structures, unremovable impurity, and easy discoloration.
Anionic polymerization of p-vinylphenol, the hydroxyl group of which is protected by tert-butyl dimethyl silyl group in advance, also has a practical disadvantage; i.e., tert-butyl dimethyl silyl chloride, which is used for the silylation, is extremely expensive.
On the other hand, the method proposed earlier by the present inventors has advantages: easy achievements of a controlled molecular weight, a controlled molecular weight distribution, and a controlled copolymer structure of alkenylphenol. In an industrial production, however, it has been found difficult to eliminate the effect of active hydrogen in such a compound as water; i.e., a precise control of molecular weight remains further to be accomplished, though the molecular weight distribution could be placed under control even in a large-scale production.